Organic light emitting diodes (OLEDs) are display devices that employ stacks of films containing organic aromatic compounds as electron transport layers (ETLs) and hole transport layers (HTLs). New material discovery for electron transport layer (ETL) and hole transport layers (HTL) in organic light emitting diodes (OLEDs) have been targeted to improve device performance and lifetimes. In the case of the HTL layer, the process by which the layer is deposited is critical for its end-use application. Methods for depositing the HTL layer, in small display applications, involve evaporation of a small organic compound with a fine metal mask to direct the deposition. In the case of large displays, this approach is not practical from a material usage and high throughput perspective. With these findings in mind, new processes are needed to deposit HTLs that satisfy these challenges, and which can be directly applied to large display applications.
One approach that appears promising is a solution process which involves the deposition of a small molecule followed by crosslinking or polymerization chemistry. There have been extensive efforts in this area, along these lines; however these approaches have their own shortcomings. In particular, the mobility of the charges in the HTL layer becomes reduced, as a result of crosslinking or polymerization chemistry. This reduced hole mobility leads to poor device lifetime and difficulty in maintaining a charge balanced device. This imbalance can also lead to device efficiency issues.
Benzocyclobutene (BCB) chemistries and their use in OLEDs are described in the following: US20040004433, US20080315757, US20080309229, US20100133566, US20110095278, US20110065222, US20110198573, US20110042661, JP2010062120, U.S. Pat. No. 7,893,160, US20110089411, US20070181874, US20070096082, CN102329411, US20120003790, WO2012052704, WO2012175975, WO2013007966, International Application PCT/CN14/084915 (filed Aug. 21, 2014), U.S. Prov. 62/039,935 (filed Aug. 21, 2014).
In the case of styrene-based chemistries, the use of the styrene moiety has been described in the following: U.S. Pat. No. 8,283,002B2; US20120049164A1; KR2012066149A (Abstract); US20090321723A1; WO2011133007A2; JP2004303488A (Abstract); US20080153019A1; WO2011062802A1; WO2009133753A1; U.S. Pat. No. 8,343,636B2; Jen et al., Chem. Mater. 2008, 20, 413-422; Kido et al., Organic Electronics, 2013, 14, 1614-1620; Meerholz et al., Adv. Funct. Mater. 2013, 23, 359-365.
However, there remains a need for new compositions for improved hole-transporting materials, and for improved processing of the same. These needs have been met by the following invention.